1. Field of the Invention
This invention relates to data transfer mechanisms and more particularly to multiple-channel serial data transfer mechanisms.
2. Description of the Related Art
Computer architectures generally include a plurality of input/output devices interconnected by one or more various buses. For example, modern computer systems typically include a central processing unit (CPU) coupled through bus interface logic to a high bandwidth system bus, such as the peripheral component interconnect (PCI) bus. Examples of devices which may be coupled to the system bus include cameras, microphones, speakers and telephony devices.
Personal computer systems were originally developed for business applications such as word processing and spread sheets, among others. However, personal computer systems are currently being used to handle a number of real time applications including multimedia applications having video and audio components, video capture and playback, telephony applications, and speech recognition and synthesis, among others. These real time applications typically require a large amount of system resources and bandwidth. One problem that has arisen is that computer systems originally designed for business applications are not well suited for the real time requirements of modern multimedia applications. For example, modern personal computer system architectures still presume that the majority of applications executing on the computer system are non-real-time business applications such as word processing, which execute primarily on the main CPU. In general, computer systems have not traditionally been designed with multimedia hardware as part of the system, and thus the system is not optimized for multimedia applications. For example, multimedia devices such as cameras, microphones and speakers are typically connected via a system bus, such as a PCI bus, which is not designed for real time applications.
In many cases, the system bus does not have the required bandwidth, throughput or response time for multimedia transfers. For example, a multimedia hardware device situated on the PCI bus must first arbitrate for control of the PCI bus before the device can begin a data transfer or access to the system memory, which introduces bus latency that may be critical in real-time applications. For example, audio data sampled at 44.1 kHz stereo provides a data sample every 11 microseconds. In this example, the latency of the system bus must be less than 11 microseconds, which is difficult to achieve with an arbitrated system bus with many components situated on the bus. In addition, since the computer system architecture is not optimized for multimedia, multimedia hardware devices are generally required to share bus usage with non-real time devices, which can severely burden the bandwidth of the bus. For example, a system bus with two 8 kilohertz (kHz) telephony data inputs and one 44.1 kHz stereo audio input produce 1.5 Mbps, which can greatly burden a serial bus.
As multimedia applications become more prevalent, multimedia hardware will correspondingly become essential components in personal computer systems. Therefore, an improved data transfer mechanism is desired which is optimized for real time multimedia and communications applications as well as for non-real time applications. In addition, improved methods are desired for transferring real time data between a multimedia device and a processor.